(1) Field of the Invention
A magnetic bubble memory device has advantageous features in that the data memorized therein is non-volatile and can be easily rewritten; functional reliability is very high, since it is a solid state device with no mechanical moving parts, and storage density thereof is very high. Therefore, use of the magnetic bubble memory device has become wide-spread in various industrial fields such as electronic exchangers, personal computers, NC (numerical control) devices, and OA (office automation) machinery.
A magnetic bubble memory device having a memory capacity of up to 4 Mbits is already commercially available, and a device having 16 Mbits memory capacity is now under development. Desirably, these magnetic bubble memory devices having a small size and high memory density will be mass-produced at a low cost to compete with other memory devices such as semiconductors and floppy discs.
(2) Description of the Related Art
Attempts have been made to obtain a bubble memory device having high memory capacity by improving the construction of the bubble memory chip itself, by greatly reducing the bubble diameter or providing a dense, miniaturized arrangement of the permalloy patterns or ion injection patterns constituting the bubble tracks. As a result, the above mentioned 4 Mbits capacity device was developed and marketed.
Also, a magnetic bubble memory device comprising a plurality of bubble memory chips disposed on a same substrate has been proposed to increase the memory capacity of the device.
However, the required high memory capacity memory chip having a desired small size has not yet been achieved, since the desired miniaturized pattern can not be formed by the conventional techniques. Therefore, the conventional bubble memory chip has a large size, which inevitably enlarges the size of the bubble memory device since the conventional bubble memory device comprises one or more bubble memory chips disposed on a same plane.
Therefore, when such a device is mounted on a printed circuit board, the device occupies a large area of the printed circuit board, and when the device is assembled within a bubble memory cassette, the cassette must be enlarged.
The conventional bubble memory device comprises: an E-shaped chip mounting plate; X and Y solenoid coils wound perpendicularly to each other on the chip mounting plate; an insulation housing in which the chip mounting plate is housed with a magnetic shunt plate and a bias magnetic plate; a plurality of outer leads disposed in a dual-in-line package (DIP) form on the housing; and a magnetic shielding case covering the housing.
In the conventional method for producing the magnetic bubble memory device, constituent parts, such as the bubble memory chip, X and Y solenoid coils, Z coil, the magnetic shunt plate, the bias magnetic plate, the shield case, and the insulation housing with outer leads, are supplied to an assembly line in series, in a predetermined sequence. However, the conventional method requires a number of complicated fabrication steps, and much time. Thus, low fabrication reliability and high cost of the products is inevitable.